1. Field
The present application relates to the field of image processing and, in particular, to temporally coherent local tone mapping of high dynamic range video.
2. Description of the Related Art
New moving image technologies for video and film have enhanced user experience via increased spatial resolution formats, such as high-definition and 4K, increased temporal resolution, such as 48 frames per second and higher for cinematic releases, and stereoscopic three-dimensional (3D) imagery, where depth provides an additional dimension. While image fidelity has advanced in terms of spatial resolution, temporal resolution, and depth, the dynamic range of moving images has received relatively little attention until recently. High-end cameras are now becoming available that are capable of capturing high dynamic range (HDR) video natively, at up to 16 f-stops of range.
However, consumer-level HDR display technology, capable of reproducing the full dynamic range of captured HDR video, is not yet available. Consequently, HDR images are typically processed before the images are distributed to and displayed by consumer devices, in order to accommodate the restricted capability of current consumer displays. One approach, as used in still photography, is tone mapping. With tone mapping, chromaticity and luminance from the source image are mapped to a more limited chromaticity and luminance set in the destination image in order to preserve some of the beneficial qualities of the original HDR imagery, while accommodating the limited dynamic range of consumer displays. In some cases, an HDR image is separated into a “base layer” image and a “detail layer” image which are compressed separately and then later recombined. One potential drawback with this approach is that tone mapping techniques from still imagery do not account for the temporal nature of video and film, leading to undesirable temporal artifacts. Another potential drawback with this approach is that the decomposition process results in undesirable “halo” effects that are not adequately eliminated with current techniques. As a result, such approaches are currently not capable of reproducing high-quality HDR moving images for display on consumer-level displays without introducing undesirable artifacts.